Nowadays, rare decays, and in particular the decays \(B_{d}\rightarrow K^{\ast }\mu ^{+}\mu ^{-}\)  and \(B_{s}\rightarrow \phi \mu ^{+}\mu ^{-}\) , are
of particular interest as they are the object of intense experimental scrutiny by the LHCb Collaboration [1]}. Updated values
of experimental branching ratios for these decays
have been published [2]} and their numerical values are given by,
\(\mathrm {Br} (B_{d}\rightarrow K^{\ast }\mu ^{+}\mu ^{-})&=&(1.06\pm 0.09)\times 10^{-6}, \\\mathrm {Br} (B_{s}\rightarrow \phi \mu ^{+}\mu ^{-})&=& (7.6\pm 1.5)\times 10^{-7} \ .\) 
